1. Field of the Invention
The present invention relates to a magnetic recording medium, a method of producing the same and magnetic recording and reproducing device having a perpendicular magnetic film with an axis of easy magnetization which is oriented mainly perpendicularly with respect to the substrate.
2. Description of the Related Art
Recording media which are presently available on the market are mainly in-plane magnetic recording media having an axis of easy magnetization of the magnetic film oriented mainly parallel to the substrate.
For longitudinal magnetic recording media, in order to achieve high recording densities, it is necessary to attempt to reduce the noise by decreasing the particle diameter of the magnetic crystal grains, but if the particle diameter of the magnetic crystal grains is reduced, because the volume of the grains is reduced, deterioration in the reproducing characteristics can readily occur due to thermal fluctuations. Furthermore, when increasing the recording density, the noise of the medium can increase due to the effect of demagnetizing fields at the recorded bit boundaries.
In contrast, for a so-called perpendicular magnetic recording media, which have an axis of easy magnetization of the magnetic layer oriented mainly perpendicularly to the substrate, even if the recording density is increased, there is little effect from demagnetizing fields at bit boundaries, and because the boundaries can form sharply defined magnetic recording domain, the noise can be reduced.
Moreover, because high recording densities can be achieved for perpendicular magnetic recording media with relatively large crystal grains, the resistance to thermal agitations can also be increased, and as a result, they have attracted much attention in recent years. For example, Japanese Unexamined Patent Application, First Publication No. 60-214417 discloses a perpendicular magnetic recording medium wherein Ge and Si are used as materials for an underlayer for a perpendicular magnetic layer comprising a Co alloy.
Particularly, by combining a perpendicular two layer medium provided with a soft magnetic underlayer with a single-pole magnetic head, it is possible to obtain efficient reproducing. However, when this two layer medium is used, spike noise is observed from the magnetic domain walls of the soft magnetic underlayer, and the error rate increases. In order to solve this problem, Japanese Unexamined Patent Application, First Publication No. Hei 7-129946, discloses a method of providing a hard magnetic underlayer between the substrate and the soft magnetic underlayer in order to reduce the spike noise. Further, Japanese Patent Application No. Hei 10-214719 discloses a method of reducing the spike noise by using an Mn type antiferromagnetic material as the soft magnetic underlayer. Alternatively, Japanese Unexamined Patent Application, First Publication No. Hei 11-149628 discloses a method of suppressing the generation of spike noise by forming a backing layer having a structure having no magnetic domain walls wherein magnetic domains are not formed.
However, in the method disclosed in Japanese Unexamined Patent Application, First Publication No. 7-129946, the thickness of the hard magnetic underlayer must be 100 nm or more, and forming a layer of this thickness requires a very long time, which is not practical in terms of productivity. Further, noise due to the hard magnetic underlayer is detected by the magnetic head, giving rise to problems such as an unacceptable error rate. Further, in the method disclosed in Japanese Patent Application No. 10-214719, after forming the Mn type antiferromagnetic material into a film, it must be annealed in a magnetic field, and because it is necessary to add an annealing treatment, and because this annealing requires a long time, problems arise, such as reduced productivity. In the method disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 11-149628, there is the problem that as the film thickness of the backing layer is increased, the medium noise increases and the error rate increases.